The flu shot, it might be said, is the black sheep of the vaccine family. In good years, people ignore it because they think the flu is no big deal. In bad years -- like this one -- they complain that it doesn't work well enough.

But the biggest problem, says Dr. Gregory Poland, a leading vaccine researcher, is that scientists are still scrambling to understand the elusive virus and come up with a better alternative. And that means that every flu season, officials confront the challenge they're facing this year as deaths and hospitalizations mount: pleading with the American people to rally behind their best line of defense.

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"Like every single man-made product, influenza vaccine is imperfect," said Poland, head of the Vaccine Research Group at the Mayo Clinic. "But I liken it to seat belts. Who would want to be in a crash without a seat belt?"

The truth is that the flu shot, with all its imperfections, is as vexing to scientists like Poland as it has been to the general public.

Federal officials estimate that this year's flu vaccine is only about 60 percent effective. That's better than nothing, notes Dr. Edward Ehlinger, the Minnesota health commissioner. But, he admits, "I think we're all in agreement that we need a much better vaccine."

Poland, who has studied vaccines for 25 years, says there are plenty of reasons that a particular vaccine might not work.

"Not all people respond to all vaccines," he said. In his own research, for example, he found that 10 percent of children have little or no response to the measles vaccine, apparently due to a genetic quirk.

Age makes a difference, too. Scientists have discovered that the older we get, the weaker our immune systems become. As a result, they don't respond as well to vaccines, which are designed to rev up the immune system to fight off disease.

It's even trickier when it comes to the flu, Poland said. Unlike measles, the flu virus changes constantly -- so it becomes a moving target for vaccine designers.

When the flu vaccine goes into production, often early in the year, scientists have to guess which strains will be circulating among the general population six to nine months later. And by that time, the virus might have changed again.

"It's why we have to give (a different) vaccine every year," Poland said.

Eventually, Poland says, that should change. Scientists are working on what some call the "Holy Grail" of flu shots -- a universal vaccine that would have to be given only two or three times in a lifetime.

Those vaccines, which are in early testing, target microscopic bits of the influenza virus that don't change from year to year. But realistically, he said, it might take up to 10 years before a universal flu vaccine is ready for prime time.

In the meantime, Poland says, new flu vaccines have come on the market designed especially for older patients (with quadruple the regular dose) and the needle-averse (a micro-shot). And future flu vaccines might be available by patch.

But until they find a way to eliminate the annual flu shot, he said, they'll always encounter resistance.

"You hear people say, 'It's just the flu ... I'm not going to get the vaccine unless I hear that it's a really bad year,'" Poland said.

"And this weighs on me heavily. Every year, people have to die and be hospitalized before the population tends to take it seriously."

Ehlinger says it's a tough message to get across, but flu shots aren't just about individual protection.

"It's not just about you getting protected, but the people around you," he said.

Studies have shown, for example, that vaccinating children can lower the risk of disease among their grandparents.

"Our message is that we need to take flu seriously because it is a serious illness," said Ehlinger. "And the best protection that we do have, although it's not perfect, is flu vaccine."

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